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MAMMALIA. 



CONTRASTS BETWEEN THE TWO SUB-ORDERS OF 

 LIVING CETACEANS. 



Mvstacoceti or Bal^enoidea, 

 baleen Cetaceans. 



The teeth are absorbed before birth. 



Whalebone or baleen-plates develop as 

 processes from the palate. 



The skull is symmetrical. 



The nasals roof the anterior nasal pas- 

 sages, which are directed upwards 

 and forwards. 



The maxilla does not overlap the orbital 

 process of the frontal. 



The lachrymal is small, and distinct 

 from the jugal. 



The tympanic is ankylosed to the peri- 

 otic. 



The rami of the mandible are arched out- 

 wards, and have no true symphysis. 



All the ribs articulate only with the 

 transverse processes of the vertebrae. 



The sternum is a single piece, and arti- 

 culates with a single pair of ribs ; the 

 sternal ribs are not ossified. 



The external nostrils are separate. 



The olfactory organ is distinctly de- 

 veloped. 



There is a short caecum. 



Examples. — 



The right-whale {BaltznaY the 

 hump - back (Megaptera), the 

 rorqual (Balcenoptera). 



Odontoceti or Dei.phinoidea, 

 toothed Cetaceans. 



The teeth persist after birth, and are 

 generally numerous and functional. 



There is no baleen. 



The skull on its upper surface is more 

 or less asymmetrical. 



The nasals, always small, do not roof 

 the anterior nasal passages, which are 

 directed upwards and backwards. 



The maxilla covers most of the orbital 

 process of the frontal. 



The lachrymal is fused to the jugal, or 

 is large, and helps to roof the orbit. 



The tympanic is not ankylosed to the 

 periotic. 



The rami of the mandible are straight, 

 and form a symphysis. 



Several anterior ribs articulate by capi- 

 tula with the centra of vertebra?. 



The sternum has usually several seg- 

 ments, with which several usually 

 ossified sternal ribs articulate. 



The nostrils unite in a single blow-hole 

 on the top of the head. 



The olfactory organ is rudimentary or 

 absent. 



There is no caecum, except in Plata- 

 nista. 



Examples. — 

 The Sperm-whale (JPhyseter), the 

 dolphin (Deipkinus), the por- 

 poise (P/tocana), the "Gram- 

 pus " (Oreo), the Ca'ing-whale 

 \Globicepkalus\ Grampus t the 

 narwhal (Monodon), with a 

 horn-like tusk in the male only, 

 the beluga {Delphinapterus\ 

 the blind Platanista of the 

 Ganges. 



In regard to the possible affinities of the Cetacea, it seems probable 

 that they are related, though not very closely, to the Ungulates. 



